In the semiconductor industry, there is no doubt that the most popular product is Metal Oxide Semiconductor Field Effect Transistor (hereinafter “MOSFET”). In recent years, due to the better characteristics, the trench MOSFET is progressively used in replace of the conventional MOSFET.
One of the trench MOSFETs, which is a trench MOSFET with a shielded gate structure, includes a shielded electrode, so that the Gate-Drain capacity is effectively reduced and the breakdown voltage of the transistor is effectively improved. As a result, the trench MOSFET with a shielded gate structure becomes more important development in the semiconductor industry.
Please refer to FIG. 1A to FIG. 1C. FIG. 1A to FIG. 1C schematically illustrate the structures corresponding to the steps of a conventional method for forming a shielded gate on a MOSFET of the prior art. The conventional method for forming a shielded gate on a MOSFET includes steps as follows. At first, depositing a hard mask layer 11 on a semiconductor substrate 1, and patterning a trench photo on the semiconductor substrate 1 and the hard mask layer 11. Next, Etching the hard mask layer 11. Then, photolithographing the trench photo (i.e. the yellow light process) for forming a trench 12. Next, etching the trench 12 (e.g. dry etching) for forming the structure as shown in FIG. 1A.
After removing the hard mask layer 11, forming a bottom gate oxide 121, depositing a shielded gate poly layer 122, and etching back the shielded gate poly layer 122 for forming the structure as shown in FIG. 1B. Next, after the structure shown in FIG. 1B is formed, processing a high density plasma (HDP) oxide deposition and processing a chemical mechanical polishing (CMP) for forming an inter-poly oxide 123. Finally, depositing a gate oxide 124 and a gate poly 125 for forming the structure as shown in FIG. 1C.
A conventional MOSFET with a shielded gate structure is manufactured by the above-mentioned method of prior art. However, the manufacturing cost of the chemical mechanical polishing method of the conventional method is relatively high and not easy to reduce, which causes the high cost of manufacturing a MOSFET.
There is a need of providing a method for forming a shielded gate of a MOSFET to obviate the drawbacks encountered from the prior art.